FIGS. 1 and 2 show two different ratchet wheel designs according to the prior art. These ratchet wheels are made through latching and milling processes, having R-angle or straight teeth. The teeth of these ratchet wheels wear quickly as used for a longer time and have low torque values. Further, when the prior art wrench is engaged with the toothed stop block in the box of the wrench, but, in this prior art, output force is not fully transferred from the wrench to the ratchet wheel and then to a workpiece. FIG. 3 shows still another design of ratchet wheel according to the prior art. According to this design, the ratchet wheel has a disk-like reinforcing structure integrally formed with the teeth at one end to reinforce the structural strength of the teeth. In either of the aforesaid three prior art ratchet wheel designs, the two distal ends of each teeth of the ratchet wheel art has right angles with respect to the base locating the teeth. When the wrench is twisted to rotate a workpiece, the teeth of the ratchet wheel may break easily, and the friction between the ends of each teeth of the ratchet wheel and the inside wall of the box of the wrench affects the performance of the wrench. Another drawback of the aforesaid prior art ratchet wheel designs is the difficulty in installing the C-shaped retainer ring. Because if the width of the two distal ends of the C-shaped retainer ring that secures the ratchet wheel in the box of the wrench is equal to the width of the locating groove of the ratchet wheel, it is not easy to fasten the C-shaped retainer ring to the locating groove of the ratchet wheel. Furthermore, because the pressure angle of the aforesaid prior ratchet wheel designs is 14.5° or 20 degrees, the engagement between the teeth and the stop block is not in coincidence with the pressure line, resulting in weak structural strength.